The additional safety provided by reflective elements on tires is well known. Such elements are provided on the sidewalls of tires to make a vehicle more readily identifiable in a side view at night; and in the grooves of tires to make a vehicle more readily identifiable in an end view at night. This invention is directed to reflective circumferentially continuous grooves in the tread of a tire, to provide better visibility and cosmetic enhancement over and above that provided by tail lights on a vehicle, and especially directed to retreaded tires used on large trucks.
U.S. Pat. No. 3,946,782 to Petrasek et al provides reflective elements in adjacent circumferential grooves of a tread so they provide an indication of the speed at which the tire is rotating—a particularly helpful feature at night when a person with impaired depth perception has difficulty estimating the speed of approaching or retreating lights mounted on a vehicle. Though they state that “These reflective elements are preferably molded into the tire during the vulcanizing or curing operation.”, and “Great care must be taken in this method so that the reflective elements are properly located on the external surface of the green tire to correspond with the desired locations in the molded, cured product;”, they failed to disclose how one might position a strip in the grooves of a hot mold. They also failed to realize that it was critically important to isolate the reflective elements from the tread surface with an effective barrier layer. This oversight is confirmed by the disclosure that “Alternatively, the reflective elements may be placed on the protrusion of the mold itself (sic)” and “The reflective elements will be transferred to and vulcanized to the finished product during the curing operation.” (col 3, lines 54–67). Clearly there is no suggestion how one might position a bead-coated strip, bead side against the hot vertical circular face of a “protrusion” of the mold (of the male portion of the mold which will form a groove) and have the strip remain in position. The statement that “Possibly, the elements may also be cemented onto the finished tire after it has been molded.” (col 4, lines 3–4) ignores the fact that it is impractical to do this by any known method, and if done, there is no disclosure as to what type of adhesive will keep the strip securely in place when the tire is on a vehicle travelling at high speed on a highway.
Aside from dealing with the problem of staining, one skilled in the art will appreciate that cementing elastomeric strips into the valleys of grooves in a cured tire is impractical. Equally impractical is trying to secure strips in the circumferential grooves of a typical tire retreading mold lying open in a generally horizontal plane (so that the tread lies in a generally vertical plane), the mold being in a curing press, as the strip is easily displaced when the green retread is cured. By “displaced”is meant that the strip does not lie flat on the floor of the valley of the groove and portions of the strip are forced over onto the sides of one or the other opposed walls of the groove, asymmetrically, usually on the lower surface of one or the other walls.
U.S. Pat. No. 3,382,908 to Palmquist et al discloses a tire on which glass beads are cured to the sidewall using a laminate of neoprene and disclosing various other vulcanizable materials none of which is identified as being impermeable to staining-components present in the rubber of the sidewall. Staining is not a severe problem in a sidewall compound; many sidewall compositions are non-staining. They also state “However, reflective treatments using reflex-reflective elements embedded in rubber, such as neoprene, natural and styrene-butadiene rubber, exhibit useful but less durable properties.” (see col 5, lines 57–60).
Though the glass beads on the sidewall are stated to be abrasion resistant and relatively durable, they are nevertheless subject to damage when the sidewall scuffs a curb. Commonly available substrates, in which retroreflective glass beads are embedded, are relatively degradable in direct sunlight, such degradation being due to staining. Since the sidewall of a tire is exposed to far more direct sunlight than the valleys in the grooves of a tread it is more susceptible to uv degradation.
Still further, when muddied or coated with road dust, the glass beads on a sidewall are not self-washing unless the tires are run through water deep enough to bury the sidewalls; so muddied glass beads on sidewalls must be washed, as is typically done in a “car wash”. There is no suggestion that the strip be placed in the valleys of grooves in a tread where the strip is susceptible to staining by ingredients in a “retread compound”, and Palmquist et al were evidently unaware of the pitfalls and advantages of so doing. Pitfalls include positioning the strip in the curing mold so it is molded substantially precisely in a groove, and choosing a thermally stable, non-staining elastomer for a substrate; advantages include having the strip protected against damage by direct sunlight and abrasion when tires are run on hard pavement, as large trucks usually are, and having a strip which is self-washing.